Microsoft Security Advisory CVE-2019-1075: ASP.NET Core Spoofing Vulnerability

Executive summary

Microsoft is releasing this security advisory to provide information about a vulnerability in ASP.NET Core 2.1 and 2.2. This advisory also provides guidance on what developers can do to update their applications to remove this vulnerability.

Microsoft is aware of a spoofing vulnerability that exists in ASP.NET Core that could lead to an open redirect. An attacker who successfully exploited the vulnerability could redirect a targeted user to a malicious website.

To exploit the vulnerability, an attacker could send a link that has a specially crafted URL and convince the user to click the link.

The update addresses the vulnerability by correcting how ASP.NET Core parses URLs.

Discussion

Discussion for this issue can be found at dotnet/aspnetcore#12007

Mitigation factors

Microsoft has not identified any mitigating factors for this vulnerability.

Affected software

Any ASP.NET Core based application that uses any of following vulnerable packages:

Advisory FAQ

How do I know if I am affected?

The affected assemblies are part of .NET Core. If you are running a vulnerable version of .NET Core you may be affected.

How do I fix the issue?

To fix the issue please install the latest version of .NET Core. If you have multiple versions of .NET Core installed you will need to install multiple runtimes, or SDKs depending on what you have installed.

If you have .NET Core 2.0 or greater installed, you can list the versions you have installed by running the dotnet --info command. You will see output like the following;

.NET Core SDK (reflecting any global.json):
 Version:   3.0.100-preview3-010431
 Commit:    d72abce213

Runtime Environment:
 OS Name:     Windows
 OS Version:  10.0.18362
 OS Platform: Windows
 RID:         win10-x64
 Base Path:   C:\Program Files\dotnet\sdk\3.0.100-preview3-010431\

Host (useful for support):
  Version: 3.0.0-preview3-27503-5
  Commit:  3844df9537

.NET Core SDKs installed:
  2.1.604 [C:\Program Files\dotnet\sdk]
  2.2.202 [C:\Program Files\dotnet\sdk]
  3.0.100-preview3-010431 [C:\Program Files\dotnet\sdk]

.NET Core runtimes installed:
  Microsoft.AspNetCore.All 2.1.11 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.All]\
  Microsoft.AspNetCore.All 2.2.3 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.All]
  Microsoft.AspNetCore.App 2.1.11 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
  Microsoft.AspNetCore.App 2.2.3 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
  Microsoft.AspNetCore.App 3.0.0-preview3-19153-02 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
  Microsoft.NETCore.App 2.1.11 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
  Microsoft.NETCore.App 2.2.3 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
  Microsoft.NETCore.App 3.0.0-preview3-27503-5 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
  Microsoft.WindowsDesktop.App 3.0.0-preview3-27504-2 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]

To install additional .NET Core runtimes or SDKs:
  https://aka.ms/dotnet-download

• For machines running .NET 2.1 you should download Runtime 2.1.12 or SDK 2.1.508 for Visual Studio 2017 or SDK 2.1.605 for Visual Studio 2019 (v16.0) or SDK 2.1.701 for Visual Studio 2019 (v16.1) from https://dotnet.microsoft.com/download/dotnet-core/2.1
• For machines running .NET 2.2 you should download Runtime 2.2.6 or SDK 2.2.108 for Visual Studio 2017 or SDK 2.2.205 for Visual Studio 2019 (v16.0) or SDK 2.2.301 for Visual Studio 2019 (v16.1) from https://dotnet.microsoft.com/download/dotnet-core/2.2

If you have both 2.1 and 2.2, you need to install updates for both versions.

Once you have installed the updated runtime or SDK, restart your apps for the update to take effect.

If you have pinned your application to a specific version of the runtime, you must update your app, recompile and redeploy it for the update to take effect.

Other Information

Reporting Security Issues

If you have found a potential security issue in .NET Core, please email details to secure@microsoft.com. Reports may qualify for the .NET Core Bug Bounty. Details of the .NET Core Bug Bounty including terms and conditions are at https://aka.ms/corebounty.

Support

You can ask questions about this issue on GitHub in the .NET Core or ASP.NET Core organizations. These are located at https://github.com/dotnet/ and https://github.com/aspnet/, respectively. The Announcements repo for each product (https://github.com/dotnet/Announcements and https://github.com/aspnet/Announcements) will contain this bulletin as an issue and will include a link to a discussion issue. You can ask questions in the discussion issue.

Disclaimer

The information provided in this advisory is provided "as is" without warranty of any kind. Microsoft disclaims all warranties, either express or implied, including the warranties of merchantability and fitness for a particular purpose. In no event shall Microsoft Corporation or its suppliers be liable for any damages whatsoever including direct, indirect, incidental, consequential, loss of business profits or special damages, even if Microsoft Corporation or its suppliers have been advised of the possibility of such damages. Some states do not allow the exclusion or limitation of liability for consequential or incidental damages so the foregoing limitation may not apply.

Acknowledgements

Reported through Datalust

External Links

CVE-2019-1075

Revisions

V1.0 (July 9, 2019): Advisory published.

Version 1.0

Last Updated 2019-07-09